Epileptic-type convulsions and magnesium deficiency.

Immediately following 4 h of continuous exercise at +/- 45% Vo2max in heat, a 23-year-old, well-trained man displayed epileptic-type convulsions. One week preceeding this incident, he completed an identical work test successfully under room temperature conditions. An assessment of his physiological and biochemical results indicated only one abnormality: during exercise in heat, an abnormally low serum magnesium concentration prevailed for most of the test. Treatment with phenobarb and magnesium chloride enteric tablets ("Slow Mag", 2 x 535 mg/d) reversed the biochemical abnormality. After checking his resting serum magnesium, the subject subsequently heat acclimatized and repeated similar treadmill tests as before without any ill effects.